Field of the Invention
The present invention relates to image forming apparatus for use with a roll of paper, and more particularly to such an apparatus wherein a roll of paper as accommodated in a case is used for forming images thereon and which is adapted to indicate the amount of paper remaining in the case.
Description of the Prior Art
Roll-type photosensitive materials such as film, photographic paper and the like for use in image exposing apparatus are accommodated in light-tight cases so as to be handleable in a lighted room despite their photosensitivity. The roll-type photosensitive material is used with the case mounted in the main body of the exposing apparatus. Such a roll-type photosensitive material is accommodated in the case by the user, or is available as accommodated by the manufacturer in a disposable case which is to be discarded after the material has been used up. To reduce cost, the disposable case has a very simple construction and is generally made of paper or the like.
When a case in use, and still containing a quantity of roll-type photosensitive material, is to be replaced by another case to use a different kind of photosensitive sensitive material contained therein, the user must accurately determine the amount of remaining material. The need to detect the remaining amount arises, for example, because if a case with only a very small amount of remaining photosensitive material is used for making a plurality of copies by a continuous image forming operation, it is likely that the case will run out of the material before the desired number of copies are obtained. Nevertheless, it is impossible to accurately recognize the amount of the remainder from outside the light-tight case accommodating the material to prevent the deterioration thereof. A weighing scale, if employed, of course accurately indicates the amount, but it is then necessary to prepare the weighing scale and to remove the case from the apparatus body before the measurement, hence a cumbersome procedure.